Try it without the motor to see if the relay is working. You will be able to hear it click. Try it with the moisture sensor in dry dirt then in wet dirt. If you hear nothing then try switching the wires on the relay.

I haven't tried it myself, but it should work. There is some resistance that comes with running a long distance, but I don't think a few feet will matter too much. You could always try making it wireless by connecting it to the internet or via bluetooth.

This is to show a cross cut diagram of the pieces in the aquaponics system and how they are all integrated with each other. Key parts are the the grow bed (the top portion of the barrel), the bell siphon (automatic flushing of water), and the tank (where the fish reside).